Backtrack 3 and 2

I preach kubuntu, i use it on a 1.9 GHz pc and 700MHz laptop.
For powerful laptops I think its very cleaver when switching to power mode as it will lower your clock speed, dim the screen etc it just has so many cleaver ways of saving power.
Plus KDE is so much better than Gnome.

I cannot think of a distro that has even been in my view a good comparrison.
Others that I recommend checking out is Fedora KDE version and PCLinuxOS I had fun with that one.
Practicality kubuntu all the way.